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  <script>
    var freqAlphabets = function (s) {
      let res = '', chars = 'abcdefghijklmnopqrstuvwxyz'
      for (let i = s.length - 1; i >= 0;) {
        if (s[i] === '#') {
          res = chars[s.substring(i - 2, i) - 1] + res
          i -= 3
        } else {
          res = chars[s[i] - 1] + res
          i -= 1
        }
      }
      return res
    };
    console.log(freqAlphabets("10#11#12"));
  </script>
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